Ann Rheum Dis: first published as 10.1136/ard.43.3.411 on 1 June 1984. Downloaded from

Annals of the Rheumatic Diseases, 1984, 43, 411-415

Some observations on the pharmacology of 'deep-heat', a topical rubifacient

A. J. COLLINS,' 2 L. J. NOTARIANNI,l E. F. J. RING,2 AND M. P. SEED1 From the 'Pharmacology Group, School ofPharmacy and Pharmacology, University ofBath, and the 2Royal National Hospital for Rheumatic Diseases, Bath

SUMMARY A topically applied rubifacient delivered by aerosol (Deep-Heat) was studied. After spray application to the forearms of volunteers, without massage, the erythema produced was measured by thermography and correlated with the concentration of 2 salicylate components ofthe mixture found in local and systemic venous . Maximum erythema occurred at about 30 minutes, while blood salicylate levels were maximal between 20 and 30 minutes after application. was absorbed before . Over the time period of the erythematous response oxygen levels in local venous blood were raised. Finally, collected from venous blood draining from the sprayed site, when induced to clump by the addition of in an aggregometer, showed increased resistance to clumping when compared with control cells. The mechanism of these observed phenomena and the mode of action ofthe constituents of Deep-Heat are discussed. copyright.

The British National Formulary lists 26 preparations This study used a preparation delivered by aerosol under the heading of rubifacients.' These mixtures which avoided the need to rub the skin. Thus we did are normally applied to and rubbed into the skin over not mechanically alter the skin by application of the an affected part, and are used by the public to treat rubifacient. We have attempted to show whether any muscular aches and pains. They are generally acknow- constituents of the applied mixture were systemically http://ard.bmj.com/ ledged to act by counterirritancy, but there is no absorbed and, if so, to measure the time course of this evidence to suggest that they act on any fundamental effect compared with other pharmacological effects. disease process. Indeed it is probable that the act of Because of the recognised effect of salicylate on the rubbing is an important part of their effective system of platelets, an action on these mechanism. cells was chosen to demonstrate an effect at the cellu- In spite of the lack of proved efficacy of these lar level. We did not attempt to demonstrate any preparations patients with clinically defined beneficial clinical effect of application on inflamed or on September 25, 2021 by guest. Protected rheumatoid arthritis, treated by a rheumatologist painful tissue. with oral anti-inflammatory drugs, superimposed rubs and linaments on to this conventional treatment Materials and methods by choice,2 and there is evidence that this practice is normal.3 The subjects used in this study were volunteers aged The majority of rubifacients contain a mixture of between 20 and 40 years. They had not taken substances to achieve a number of effects when or other anti-inflammatory medicines during 2 weeks rubbed into the skin: an agent to produce a 'medical prior to the study. smell', an agent to produce an erythematous reaction Rubifacient formulation (Deep-Heat). The rubi- and irritant response from the skin, and an anti- facient mixture was produced in an aerosol can. The inflammatory agent, normally a salicylate. The com- commercial form of the preparation was used which bination produces an erythema and irritation which is contained the following ingredients: appreciated as a sensation of warmth. Methyl nicotinate 1-6% w/w Accepted for publication 14 July 1983. 2-Hydroxyethyl salicylate 5- 0% w/w Correspondence to Dr A. J. Collins, University of Bath, School of Methyl salicylate BP 1% w/w Pharmacy and Pharmacology, Claverton Down, Bath BA2 7AY. Ethyl salicylate 5% dw 411 Ann Rheum Dis: first published as 10.1136/ard.43.3.411 on 1 June 1984. Downloaded from

412 Collins, Notarianni, Ring, Seed These substances were in an isopropanol sol- method of Silver et al.6 Blood was collected as pre- vent, propelled by trichloro-fluoro-urethane and viously described (9 ml blood added to 1 ml citrate) dichloro-difluoromethane. and centrifuged at 200g for 10 minutes. The In addition a special aerosol was produced which rich plasma (PRP) was aspirated and stored at room delivered 100,ul of solvent per burst. temperature. Platelet aggregability was then Anatomical site of study. Deep-Heat was sprayed measured by taking a 200 Al aliquot of PRP, which from a metered aerosol on to the anterior aspect of was stirred at 1 100 rpm at 3TC in a plastic tube in a the right forearm of 12 volunteers. An area from 5 cm Malin dual channel aggregometer. Arachidonic acid above the wrist to 5 cm below the antecubital fossa (about 0 4 mM) was added to achieve a threshold was covered as evenly as possible from a distance of concentration which caused platelets to clump. 10-15 cm. When a 'therapeutic' dose was given from Platelets collected after spraying a forearm with the commercial aerosol, the area of the arm was Deep-Heat were aggregated by this method, and the thoroughly wetted with propellant. Even with appli- amount of arachidonic acid required to achieve cation from close range, as described, some of the aggregation was compared with the threshold value. aerosol sprayed beyond the arms and was lost. Thus Venous blood oxygen. Oxygen in venous blood was the amount applied to the forearm was not an exact measured using an Instrumentation Laboratories dose even when metered accurately. 113 blood gas analyser with an oxygen electrode. Venepuncture. Venous blood was drawn from a Blood from both arms of 2 volunteers was taken for vein in the right antecubital fossa when local esti- both local and systemic measurements. mations were required and from the left antecubital fossa for systemic studies. Results For measurement of constituents by high perfor- mance liquid chromatography (HPLC) plasma was When the anterior aspect of the right forearm was collected from blood placed in lithium-heparin tubes, sprayed with a small volume of Deep-Heat (500,ul), - a visible erythematous skin reaction developed then frozen at 20°C until assayed. Six volunteers copyright. were studied. within approximately 10 minutes. The reaction was For measurement of platelet aggregation venous measured by thermography, and a typical time pro- blood was collected from the right or left antecubital file of the erythema is shown in Fig. 1. The initial fall fossa via a No. 1 hypodermic needle, by gravity, into a in the index was the result of cooling owing to evap- plastic tube containing 0 5 ml of 3 8% w/v citrate. oration of aerosol vehicle from the skin. Four volunteers were studied. Concurrently, blood taken from the right antecubi- Venous blood oxygen was measured in blood tal fossa was assayed for ethyl and methyl salicylate to withdrawn in a plastic 5 ml syringe containing a bead show the extent of local absorption of these com- http://ard.bmj.com/ of 1000 Uml sodium heparin. Blood from either arm pounds. The absorption profile of both these con- was studied. stituents in local venous blood drained from the Skin erythema. Erythema of sprayed skin was sprayed site was similar to the time course of the measured by thermography. Four volunteers, with erythematous response. their right arm unclothed, remained in an ambient To assess the systemic blood levels achieved by the temperature of 20°C for 20 minutes before being salicylate components of the spray the right forearm

sprayed. The thermographic index of an area 10 by of one subject was completely wetted with the on September 25, 2021 by guest. Protected 5 cm over the anterior aspect of the forearm was then aerosol, then blood was taken from both the right and measured.45 left antecubital fossae for the next 90 minutes. The Measurement of ethyl and methyl salicylate in blood was assayed for ethyl and methyl salicylate. venous blood by HPLC. After application of the rubi- The result for one volunteer is shown in Fig. 2,and the facient to the anterior aspect of the right forearm blood results for the group given in Table 1. In this and was collected from the right antecubital fossa as other experiments the absorption ofmethyl salicylate described. The plasma was extracted with ether and preceded that of ethyl salicylate, but the latter the extract evaporated to dryness under nitrogen. appeared in venous blood at a higher concentration. The residue was taken up in and applied A comparatively high concentration of the salicylates to a Lichrosorb RP 8 10 Am column (25x4 5 cm was found in local venous blood for an hour after internal diameter), the mobile phase being acetate application, but in blood taken from the opposite arm buffer, pH 2 0 acetonitrile (60:40) with a flow rate of they were detected up to only 20 minutes after appli- 1 2 ml/ min. Detection was by light at cation and at the lower limit of the sensitivity of the 238 nm. assay. Measurement of platelet aggregation. Platelet Serial venous blood samples taken from a vein aggregation was measured by a modification of the draining a forearm sprayed with Deep-Heat became Ann Rheum Dis: first published as 10.1136/ard.43.3.411 on 1 June 1984. Downloaded from

Some observations on the pharmacology of 'deep-heat', a topical rubifacient 413

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X20 soo X E

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10 20 30 40 SO0 70 so 90 Minutes Fig. 2 Local and systemic venous blood levels ofethyl and methyl salicylate over 90 minutes after spraying the right anterior forearm with a 'therapeutic' dose ofDeep-Heat. 30 40 After spraying the right forearm sufficiently to wet the whole Minutes anterior surface, venous blood was taken from the right and left antecubital fossae. The salicylates were measured in Fig. 1 The thermographic index, measured over 70 plasma by HPLC. The subject (volunteer 3) was male, aged minutes, ofthe anterior aspect ofa right forearm after 40years. E=Methylsalicylate. OJ=Ethylsalicylate. A: Local application of500 ,ulofDeep-Heatspray. Samplesofvenous blood from right antecubital fossa. B: Systemic blood from copyright. blood taken from the right antecubital fossa over the same left antecubital fossa. period showedthe rapidabsorption ofboth ethyl and methyl salicylate as measured by high performance liquid chromatography. The subject was a white female, aged 22 Table 1 The mean local venous blood level ofethyl and years. E=Methyl salicylate. O=Ethyl salicylate. methyl salicylate over 90 minutes after spraying the right anteriorforearm with a 'therapeutic' dose ofDeep-Heat in 6 visibly bright red over the following 30 minutes. volunteers. Values represent the mean plasma level± SD of6 When the oxygen concentration in this blood was samples taken over 90 minutes from each volunteer. http://ard.bmj.com/ measured, an increase in venous blood oxygen was Conditions for the collection ofblood are stated in the text. found which showed a profile similar to the thermo- These mean values are to be compared with the plasma graphic index curve measuring erythema. No signifi- profile over 90 minutes shown in Fig. 2. cant increase in oxygen concentration took place in Volunteer Sex Mean level of Mean level of blood from the opposite arm (Fig. 3). methyl salicylate ethyl salicylate Deep-Heat was tested for its capacity to alter the in plasma in plasma clumping of platelets. The right forearm of volun- (ng(ml) (nglml) on September 25, 2021 by guest. Protected teers was sprayed with Deep-Heat and the anterior 1 F 0-233±O0165 O-164±O069 surface completely wetted. Venous blood samples 2 M 0-021± 0029 O-007± 014 were then withdrawn from the right antecubital fossa 3 M 2-296±1-490 O 874±O-520 and the harvested platelets tested for their capacity to 4 F O-390tO-212 O-618bO-454 clump in the presence of arachidonic acid (AA) in an 5 F O 169bO-224 0230±O310 6 F - 0283± 037 O0042b0-049 in-vitro test. The results obtained (Fig. 4) suggest that the platelets collected from such blood were made more resistant to AA induced clumping, but only for They usually contain salicylates and other substances a short time, the maximum effect being reached at 15 that cause a feeling of warmth and wellbeing when minutes after application of the spray. The effect was they are applied to the skin. Their effect on muscle or not seen in platelets from venous blood from the joint pain is difficult to quantitate, but some evidence opposite, untreated arm. exists that they do relieve rheumatic pain.7 If their popularity with the public is used as a gauge, they are Discussion successful medicines, with a market in the UK esti- mated to be worth £7m. However, they are not for- Rubifacient preparations are traditional mixtures. mally used to treat joint or muscle pain. Ann Rheum Dis: first published as 10.1136/ard.43.3.411 on 1 June 1984. Downloaded from

414 Collins, Notarianni, Ring, Seed state that massage is not necessary, and we relied purely on the ingredients of the mixture to achieve an effect. 4 It is difficult to know which component of the mixture caused the changes that have been -...... measured; probably nicotinate was responsible for >------Q--\---V \ the majority of the recorded vasodilatation. Crock- ford et al.8 demonstrated the effect of topically ------\B -applied nicotinate (Trafuril, tetrahydrofurfuryl nicotinic acid ) and observed that the skin of a denervated limb did not produce an erythematous response. Their findings and the observation of Peterson et al.,9 who found that lepromatous skin tO Minutes with incompetent cutaneous innervation failed to react to nicotinate, suggest that the vasodilatation is Fig. 3 Changes in oxygen concentration of venous blood mediated by a nervous reflex rather than by the direct taken from the right antecubital fossae of 2 subjects (A and action of nicotinate on the smooth muscle of blood B) over 90 miniutes. The right anterior forearms * had been vessels. The entry of topically applied nicotinate is sprayed with L)eep-Heat at zero time. For comparison, us .' ' oxygen concentrepeatioin b rootaken Foromptherleftsantecut usually via hair follicles and sweat glands and is " fossae EKthromboxane A2,. The rubbing froim the pharmacological effects of the system is inhibited by aspirin and other nonsteroidal ingredients of rubifacient preparations, both may anti-inflammatory drugs via inhibition of the have a counLterirntant effect. For the study of the cyclo-oxygenase.14 Inhibition of platelet cyclo- pharmacoloigy of the ingredients we therefore chose oxygenase by the applied salicylate mixture, and thus an aerosol f(Drm of rubifacient whose manufacturers a decrease in cellular , may be the Ann Rheum Dis: first published as 10.1136/ard.43.3.411 on 1 June 1984. Downloaded from

Some observations on the pharmacology of 'deep-heat', a topical rubifacient 415 mechanism by which this happened. This phenom- 2 Puliar T, Capell H A, Millar A, Brooks R G. Alternative enon was shown only in platelets harvested from local medicine; cost and subjective benefit in rheumatoid arthritis. Br Med J 1982; 285: 1629-31. blood. However, salicylate is a poor inhibitor of 3 Dieppe P, Doyle D, Jacoby R. Arthritis: anti-inflammatory cyclo-oxygenase, and it may be that resistance to drugs in practice. Practitioner 1981; 225: 397-9. clumping was caused by a different mechanism, for 4 Collins A J, Ring E F J, Cosh J A, Bacon P A. Quantitation of instance by the release of , a potent thermography in arthritis using multiisothermal analysis. I. The thermographic index. Ann Rheum Dis 1974; 33: 113-5. inhibitor of platelet aggregation, from blood vessel 5 Ring E F J, Collins A J, Bacon P A, Cosh J A. Quantitation of walls,"5 perhaps by the vasodilatatory effect of the thermography in arthritis using multiisothermal analysis. II. applied nicotinate. Effect of nonsteroidal anti-inflammatory therapy on the ther- None of the pharmacological effects described mographic index. Ann Rhewn Dis 1974; 33: 353-6. here may contribute to the action of this or any other 6 Silver M J, Smith J B, Ingerman C M, Kocsis J J. Arachidonic acid induced human platelet aggregation and prostacyclin for- rubifacient in the treatment of soft tissue or joint mation. 1973; 4: 863-75. pain, but the combination of counterirritancy, 7 Howell T H. The relief of rheumatic pains with diethylamine increased local blood flow owing to blood vessel dila- salicylate cream: a clinical trial. BrJ Phys Med 1955; 18: 62-3. 8 Crockford G W, Hellon R F, Heyman A. Local vasomotor tation, enhanced oxygen concentration in local responses to and ultra-violet radiation. J Physiol venous blood, and an antiaggregatory effect on 1962; 161: 21-9. platelets would suggest an anti-inflammatory action. 9 Peterson J B, Farber E M, Fulton G P. A clinical evaluation of All these effects seem to be local phenomena nicotinate rubifacients. Arch Dermatol 1960; 82: 63-8. 10 Hadgraft J W, Somers G F. Percutaneous absorption. J Pharm restricted to the treated site and we have no evidence Pharmacol 1956; 8: 625-33. that structures deeper than the skin are affected or 11 Stoughton R B, Cleveland M D. Percutaneous absorption. that there was any systemic effect. However, the Influence of temperature and hydration. Arch Environ Health changes observed were real pharmacological effects, 1965; 11: 551-4. 12 Danford D E, Munro H N. Water soluble vitamins. In: Good- illustrating that this type of medicine is not therapeut- man L S, Gilman A, eds. The pharmacological basis oftherapeu- ically inactive and may demonstrate useful phar- tics. New York: Macmillan, 1980: 1568-9.

macological principles. 13 Hamberg M, Svensson J, Samuelsson B. : a new copyright. group of biologicaily active compounds derived from prosta- We thank the Mentholatum Company Ltd for supplies of Deep- glandin endoperoxides. Proc Natl Acad Sci USA 1975; 72: Heat. 2994-8. 14 Moncada S, Vane J R. Mode of action of aspirin-like drugs.Adv References Intern Med 1979; 24: 1-22. 15 Moncada S, Vane J R. The discovery of prostacyclin-a fresh 1 British national formulary. No. 5. London: British Medical insight into arachidonic acid metabolism. In: Kharasch N, Association and Pharmaceutical Society of Great Britain, 1983: Fried J, eds. Biochemical aspects ofprostaglandins and throm-

299. boxanes. London: Academic Press, 1977: 155-77. http://ard.bmj.com/ on September 25, 2021 by guest. Protected